The present invention relates to a method of placing concrete into a steel encasement by injection for constructing a composite member of a concrete-steel structure.
There has been proposed a method of constructing an offshore platform using such composite members which are produced by placing concrete into steel encasements. Composite members provide excellent watertightness and high breaking strength to the offshore platform and make reinforcing steel and formworks unnecessary. Thus, the composite member is the most suitable for the ice-resisting member of the offshore platform.
FIG. 1 illustrates a typical example of the offshore platform, which has a deck A to be installed with equipments for drilling offshore oil wells and an octagonal supporting structure B for supporting the deck A. The supporting structure B includes ice-resisting trapezoidal slanted walls 2, rectangular vertical walls 3 for providing rigidity to the offshore platform and a bottom slab 4 on which the vertical walls 3 are erected. The bottom slab 4 is placed on the sea bed 1 for transmitting force, exerted on the vertical walls 3, to the sea bed 1. As clearly seen from FIG. 3, vertical walls 3 include multiple walls circumferentially parallel and radial walls disposed radially outwards from the central portion of the platform. As shown in FIG. 2, the slanted walls 2 and the vertical walls 3 are constructed by placing concrete 6 into their slanted steel encasements 7 and vertical steel encasements 8, respectively. As illustrated in FIG. 4A, each slanted steel encasement 7 includes a pair of parallel upper and lower wall plates 11 and 13 which are opposed to each other to form a space between them for containing concrete 6. Each vertical steel encasement 8, as shown in FIG. 4B, includes a pair of parallel outer and inner wall plates 15 and 17 opposed to each other to form a space between them for containing concrete 6. The steel encasements 7 and 8 are closed at their lateral edges with steel plates and have inner stiffeners 9 mounted in a lattice shape on the inner faces of their wall plates 11, 13; 15, 17. These inner stiffeners 9 ensure integrity of slanted and vertical steel encasements 7 and 8 to the concrete 6 placed into them. However, the inner stiffeners 9 make it difficult to fill concrete into slanted steel encasements 7 and vertical steel encasements 8 and also make compaction of the concrete placed and treatment of joints thereof difficult. As shown in FIG. 2, the slanted steel encasement 7 consists of an upper portion 7A, an intermediate portion 7B and a lower portion 7C. The vertical steel encasements 8 are named first vertical steel encasements 8A, second vertical steel encasements 8B, third vertical steel encasements 8C . . . from the outside. The heights of the second and the fourth vertical steel encasements 8B and 8D are about 30 m and 50 m respectively.
For overcoming the problem relating to infilling concrete 6 into the steel encasements 7 and 8, there has been proposed a method as illustrated in FIG. 5. For placing concrete 6 into, for instance, the second vertical steel encasement 8B, the concrete 6 is supplied by means of a chute 10 from an upper end opening 12 of an erected vertical steel encasement piece 8' into the piece 8' as illustrated in connection with the third and the fourth vertical steel encasement 8D and is compacted with a rod vibrator 14 or a like device. The concrete 6 is supplied to the chute 10 by means of a bucket 16 suspended from a crane 18. The rod vibrator 14 is inserted from the open end 12 into the vertical steel encasement piece 8' and held there by an operator on a scaffold 20 which is set beside the vertical steel encasement piece 8' as shown in connection with the vertical steel encasement 8B. After the placing of the concrete 6, another steel encasement piece 8" is carried by another crane 18 and is welded at its lower open end to the upper open end 12 of the steel encasement piece 8' into which the concrete 6 has been placed. In the same manner, concrete 6 is placed into another steel encasement piece 8". When the vertical wall 3 is erected to a predetermined height in this manner with respect to the second vertical steel encasement 8B, the lower portion 7C of the slanted steel encasement 2 is jointed to the upper ends of the first and second vertical steel encasements 8A and 8B, already filled with concrete 6, and is then filled with concrete 6 in the same manner as the second vertical steel encasement 8B.
Alternatively, concrete may be placed into slanted steel encasements 7 and vertical steel encasements 8 as illustrated in FIG. 6, in which the vertical steel encasements 8 have openings 12A formed through their inner wall plates 17 and the slanted steel encasements 7 have openings 12A formed through their upper wall plates 11. Concrete 6 is placed into the slanted and vertical steel encasements 7 and 8 through openings 12A by means of, for example, a tremie pipe 22. Then, the concrete placed is compacted with a rod vibrator 14 as in the method previously described. After this, the openings 12A, through which the concrete 6 has been placed, are closed by welding steel plates.
In the two conventional methods above stated, concrete 6 is placed by means of chutes 10 or tremies 22 which are inserted through open ends 12 or openings 12A and hence the height of concrete placing is limited by levels, to which rod vibrators 14, chutes 10 and tremies 22 can reach, as well as by allowable pressure of the concrete 6 applied to steel encasements 7 and 8. Thus, in the method in FIG. 5, concrete is placed into a steel encasement piece, to which another steel encasement piece is then welded to be disposed above it. By repeating these operations a slanted wall or a vertical wall is constructed to a predetermined height. Thus, the number of assembly operations and welding operations for constructing the slanted and vertical walls are increased, so that the construction cost and the construction period of both the slanted walls and the vertical walls are increased.
On the other hand, the method illustrated in FIG. 6 reduces the number of assembly operations and welding operations, but a large number of wide openings 12A must be formed due to the height limit of concrete placing mentioned above and closed after the placing of concrete. These also raise the construction cost and prolong the construction period. Further, chutes 10, tremie pipes 22 and other equipments must be disposed in place before the concrete placement and then removed. Such operations further increase the construction cost and period.